Microlens array, method for fabricating the same and optical devices

FIELD OF THE INVENTION

The present invention relates to a microlens array, a method for fabricating the same, and an optical device.

DESCRIPTION OF THE RELATED ART

To date, a microlens array formed by arranging a plurality of minute lenses has been applied to a liquid crystal panel, for example. By applying the microlens array, the individual lenses focus incident light into corresponding pixels. Thus, a display screen can be made bright.

The lens side of the microlens array has bumps and dips, but it is required to be flat in order to form electrodes thereon. Conventionally, a flat surface has been formed by attaching a cover glass to the lens side with, for example, an adhesive and polishing it to make it thin. However, the polishing process in particular takes a long time.

The present invention aims to solve such problems. The object thereof is to provide a method for fabricating a microlens array having a flat surface by a simple process, the microlens array fabricated thereby, and an optical device.

SUMMARY OF THE INVENTION

(1) The method for fabricating the microlens array in the invention includes a first step of bringing a lens side of a microlens array substrate having a plurality of lenses formed thereon into close contact with a flat surface of a master plate, in which one surface is the flat surface, with a light transmitting layer precursor therebetween;

a second step of curing the light transmitting layer precursor to form a light transmitting layer; and

a third step of releasing the master plate from the light transmitting layer.

According to the invention, the light transmitting layer is formed on the lens side of the microlens array substrate. The upper side of the light transmitting layer is flattened by the flat surface of the master plate. In this manner, according to the invention, a simple process in which the master plate is brought into close contact with the light transmitting layer precursor and is then released can form the light transmitting layer having a flat surface on the lens side of the microlens array substrate.

(2) This method for fabricating the microlens array may further include a step of forming at least one of a black matrix, an electrode, and an alignment layer on the light transmitting layer.

According to this, at least one of the black matrix, the electrode, and the alignment layer can be formed on the flat surface of the light transmitting layer.

(3) This method for fabricating the microlens array may further include a step of depositing a protective coating on the light transmitting layer.

According to this, even though a material having a low durability is used as the light transmitting layer, the protective coating can protect the light transmitting layer.

(4) This method for fabricating the microlens array may further include a step of forming at least one of the black matrix, the electrode, and the alignment layer on the protective coat.

According to this, at least one of the black matrix, the electrode, and the alignment layer can be formed on the protective coating that has been deposited on the flat surface of the light transmitting layer.

(5) In the method described in any one of the methods for fabricating the microlens array, the light transmitting layer precursor may include a substance which can be cured by applying energy.

(6) In this method for fabricating the microlens array, the energy may be at least one of light and heat.

(7) In the method described in any one of the methods for fabricating the microlens array, the light transmitting layer precursor may be made of a resin.

(8) The microlens array in the invention is fabricated by the methods described above.

(9) The optical device in the invention has the microlens array described above.

(10) This optical device may be a display device having a light source for radiating light toward the microlens array.

(11) This optical device may be an imaging device having an image pick-up device that lights focussed by the microlens array enters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. <b>1</b>(A) to <b>1</b>(C) depict diagrams illustrating the method for fabricating the microlens array in an embodiment in which the present invention is applied.

FIGS. <b>2</b>(A) and <b>2</b>(B) depict diagrams illustrating the method for fabricating the microlens array in the embodiment in which the present invention is applied.

<figref id="DRAWINGS">FIG. 3</figref> depicts a diagram illustrating a modified example of the embodiment in which the present invention is applied.

<figref id="DRAWINGS">FIG. 4</figref> depicts a diagram illustrating an electronic device provided with the microlens array in which the present invention is applied.

<figref id="DRAWINGS">FIG. 5</figref> depicts a diagram illustrating an electronic device provided with the microlens array in which the present invention is applied.

FIGS. <b>6</b>(A) to <b>6</b>(E) depict diagrams illustrating the steps of producing a master plate for fabricating the microlens array substrate.

FIGS. <b>7</b>(A) to <b>7</b>(C) depict diagrams illustrating the steps of producing an intermediate plate from the master plate for fabricating the microlens array substrate.

FIGS. <b>8</b>(A) to <b>8</b>(C) depict diagrams illustrating the steps of producing a replica plate from the intermediate plate for fabricating the microlens array substrate.

FIGS. <b>9</b>(A) to <b>9</b>(C) depict diagrams illustrating the steps of fabricating the microlens array substrate.

FIGS. <b>10</b>(A) to <b>10</b>(E) depict diagrams illustrating the steps of producing a master plate for fabricating the microlens array substrate.

FIGS. <b>11</b>(A) to <b>11</b>(C) depict diagrams illustrating the steps of producing a master plate for fabricating the microlens array substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, preferred embodiments of the invention will be described with reference to the drawings.

FIGS. <b>1</b>(A) to <b>2</b>(B) depict diagrams illustrating the method for fabricating the microlens array in the embodiment in which the present invention is applied. In the embodiment, the microlens array comprises a light transmitting layer formed on the lens side of a microlens array substrate having a plurality of lenses formed thereon.

A microlens array substrate <b>10</b>, a master plate <b>20</b>, and a light transmitting layer precursor <b>30</b> shown in FIG. <b>1</b>(A) are prepared. Additionally, the material for forming the layer constituting the microlens array substrate <b>10</b> may be called a first light transmitting layer precursor and the light transmitting layer precursor <b>30</b> may be called a second light transmitting layer precursor. Furthermore, the layer constituting the microlens array substrate <b>10</b> may be referred as a first light transmitting layer and a light transmitting layer <b>32</b> formed by the light transmitting layer precursor <b>30</b> may be referred as a second light transmitting layer.

The microlens array substrate <b>10</b> transmits light. A plurality of lenses <b>12</b> is formed on at least one side of the microlens array substrate <b>10</b> (in many cases, it is formed only on one side). Each of the lenses <b>12</b> shown in FIG. <b>1</b>(A) is a convex lens, but it may be a concave lens.

A flat surface <b>22</b> is formed on a master plate <b>20</b>. The flat surface <b>22</b> has an area corresponding to the area having the plurality of lenses <b>12</b> of the microlens array substrate <b>10</b> formed thereon. The master plate <b>20</b> may have the shape of the substrate; in this case, one side may be the flat surface <b>22</b>. The master plate <b>20</b> may be formed of metal, or may be formed of a light-transmitting material such as glass.

The light transmitting layer precursor <b>30</b> preferably has high light transmission because it is formed over the lenses <b>12</b> of the microlens array substrate <b>10</b>. Additionally, the light transmitting layer precursor <b>30</b> has a property for contacting the lens surface of the lenses <b>12</b> to refract light at the interface. That is, the light transmitting layer precursor <b>30</b>, when cured, has a different refractive index from that of the lenses <b>12</b> of the microlens array substrate <b>10</b>.

In the embodiment, the side formed with the lenses <b>12</b> of the microlens array substrate <b>10</b> is brought into close contact with the flat surface <b>22</b> of the master plate <b>20</b> with the light transmitting layer precursor <b>30</b> therebetween. Then, the light transmitting layer precursor <b>30</b> is spread over a predetermined region to form the light transmitting layer <b>32</b> made of the light transmitting layer precursor <b>30</b> between the microlens array substrate <b>10</b> and the master plate <b>20</b>, as shown in FIG. <b>1</b>(B).

In FIG. <b>1</b>(A), the light transmitting layer precursor <b>30</b> is placed on the side having the lenses <b>12</b> of the microlens array substrate <b>10</b> formed thereon. However, it may be placed on the master plate <b>20</b> or on both the microlens array substrate <b>10</b> and the master plate <b>20</b>. Furthermore, the light transmitting layer precursor <b>30</b> may be spread over one or both of the microlens array substrate <b>10</b> and the master plate <b>20</b> beforehand by methods such as spin coating, spray coating, roll coating, bar coating, or dipping.

The light transmitting layer precursor <b>30</b> preferably has excellent releasability from the master plate <b>20</b> and process resistance in the subsequent processes. The light transmitting layer precursor <b>30</b> may be a liquid substance or liquefiable substance. As the liquid substance, substances which can be cured by applying energy can be utilized. As the liquefiable substance, substances having plasticity can be utilized.

Additionally, when a resin is selected as the light transmitting layer precursor <b>30</b>, that having an energy curable property or plasticity is preferable.

As the resin having the energy curable property, it is desirable that the resin is curable by applying at least either light or heat. In utilizing light or heat, a commercially available photolithography machine and a heater such as a baking furnace or a hot plate can be utilized, which can save equipment costs.

As the resin having such an energy curable property, acrylic resins, epoxy resins, melamine resins, and polyimide resins, for example, can be utilized. The acrylic resins are particularly preferable because those being cured for a short time with light irradiation can be obtained easily by utilizing a variety of commercially available precursors or sensitizers (photopolymerization initiators).

As a specific example of a basic composition of the light-curable acrylic resins, prepolymers, oligomers, monomers, or photopolymerization initiators are given.

As the prepolymers or oligomers, for example, acrylates such as epoxy acrylates, urethane acrylates, polyester acrylates, polyether acrylates, and spiroacetal acrylates; and methacrylates such as epoxy methacrylates, urethane methacrylates, polyester methacrylates, and polyether methacrylates can be utilized.

As the monomers, for example, monofunctional monomers such as 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, N-vinyl-2-pyrolidone, Carbitol acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, dicyclopentenyl acrylate, and 1,3-butanediol acrylate; difunctional monomers such as 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, and pentaerythritol diacrylate; and polyfunctional monomers such as trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol triacrylate, and dipentaerythritol hexaacrylate can be utilized.

As the photopolymerization initiators, for example, acetophenones such as 2,2-dimethoxy-2-phenylacetophenone; butyl phenones such as -hydroxy isobutyl phenone and p-isopropyl--hydroxy isobutyl phenone; acetophenone halides such as p-tert-butyl dichloroacetophenone, p-tert-butyl trichloroacetophenone, and ,-dichlor-4-phenoxyacetophenone; benzophenones such as benzophenone and N,N-tetraethyl-4,4-diaminobenzophenone; benzyls such as benzyl and benzyldimethylketal; benzoins such as benzoin and benzoin alkyl ether; oximes such as 1-phenyl-1,2-propanedion-2-(o-ethoxycarbonyl)oxime; xanthones such as 2-methylthioxanthone and 2-chlorothioxanthone; and radical generating compounds such as Michler's ketone and benzyl methylketal can be utilized.

Additionally, compounds such as amines may be added for preventing oxygen from inhibiting curing, or solvent components may be added for facilitating spreading as necessary. The solvent components are not defined particularly; a variety of organic solvents such as propylene glycol monomethyl ether acetate, methoxymethyl propionate, ethoxyethyl propionate, ethyl lactate, ethyl pyruvinate, methyl amyl ketone can be utilized.

These substances are preferable because they have excellent releasability when the master plate <b>20</b> is formed of silicon or quartz having excellent flatness.

Furthermore, as the resins having plasticity, resins having thermoplasticity such as polycarbonate resins, polymethyl methacrylate resins, and amorphous polyolefine resins can be utilized. Heating such a resin at the softening point temperature or above plasticates and liquefies it. After it is sandwiched between the microlens array substrate <b>10</b> and the master plate <b>20</b>, as shown in FIG. <b>2</b>(B), the plasticated resin is cooled to cure it. Then, the light transmitting layer <b>32</b> is formed.

Moreover, when the microlens array substrate <b>10</b> is attached to the master plate <b>20</b>, pressure may be applied via at least one of the microlens array substrate <b>10</b> and the master plate <b>20</b>, as necessary. Applying pressure can shorten the period of time to spread the light transmitting layer precursor <b>30</b> over a predetermined region. Thereby, workability can be improved.

Then, curing treatment is applied in accordance with the light transmitting layer precursor <b>30</b>. For example, when a light-curable resin is used, light is radiated under predetermined conditions. Thereby, the light transmitting layer precursor <b>30</b> is cured to form the light transmitting layer <b>32</b>, as shown in FIG. <b>2</b>(B).

Subsequently, the master plate <b>20</b> is released from the light transmitting layer <b>32</b>, as shown in FIG. <b>1</b>(C) and then the light transmitting layer <b>32</b> remains on the side of the microlens array substrate <b>10</b> having the lenses <b>12</b> formed thereon. On the light transmitting layer <b>32</b>, a flat surface <b>34</b> is formed corresponding to the flat surface <b>22</b> of the master plate <b>20</b>.

After that, a protective coating <b>40</b> may be deposited on the flat surface <b>34</b> of the light transmitting layer <b>32</b>, as shown in FIG. <b>2</b>(A). The protective coating <b>40</b> is not defined particularly in case of those having resistance to the subsequent processes, but inorganic materials, for example, can be used. Specifically, glass precursors such as polysilazane and polysiloxane can form the protective coating <b>40</b>.

The protective coating <b>40</b> may be formed of a ceramic. The protective coating <b>40</b> may be formed of silicon dioxide (SiO₂) in the form of quartz glass (silicate glass). Silicon dioxide (SiO₂) has a hard surface, has excellent heat resistance, water resistance, chemical resistance, and durability, and can be formed at low cost. Colloidal silicas (silica sols) may be used for forming it. Raw materials having silica sols and silane coupling agents as principal constituents may be used. The silane coupling agents enhance adhesion to the light transmitting layer <b>32</b> which is an under layer. Additionally, surface active agents for enhancing surface wettability or catalysts for facilitating reactions may be added. The silica sols (alternatively, raw materials having silica sols and silane coupling agents as principal constituents) can be disposed evenly at low temperatures by spin coating or dipping.

Before the protective coating <b>40</b> is deposited, surface treatment (plasma treatment or silane coupling treatment, for example) for improving the adhesion or the wettability to the protective coating <b>40</b> may be applied to the surface of the light transmitting layer <b>32</b>.

The protective coating <b>40</b> is not needed in the case where the light transmitting layer <b>32</b> itself has process resistance. A microlens array <b>1</b> can be obtained in this manner.

Then, as shown in FIG. <b>2</b>(B), at least one of a black matrix <b>42</b>, an electrode (electrode film) <b>44</b>, and an alignment layer <b>46</b> is deposited on the light transmitting layer <b>32</b> or on the protective coating <b>40</b> formed thereon. The black matrix <b>42</b> is deposited by etching a film made of chromium. The protective coating <b>40</b> has process resistance to this etching process. When the light transmitting layer <b>32</b> has process resistance to the etching process, the protective coating <b>40</b> is not needed. The alignment layer <b>46</b> is deposited by disposing a material of a polyimide resin or its precursor by a coating method and firing it at temperatures of 100 to 350 C.

As the coating method, methods of spin coating, roll coating, or flexographic printing can be utilized. The firing temperatures are properly set in accordance with the materials to be used. The electrode <b>44</b> is an ITO (Indium Tin Oxide) film, for example, which is deposited by vacuum deposition such as spattering or evaporation and then annealing treatment is applied. The annealing treatment temperatures are 100 to 300 C. in general, but higher temperatures are preferable because resistance values are reduced and an excellent electrode film is deposited. Additionally, firing for depositing the alignment layer <b>46</b> and annealing treatment for the electrode <b>44</b> may be conducted at the same time.

According to the embodiment, a simple process, in which the master plate <b>20</b> is brought into close contact with the light transmitting layer precursor <b>30</b> and is released, can form the light transmitting layer <b>32</b> having the flat surface <b>34</b> on the lenses <b>12</b> of the microlens array substrate <b>10</b>.

<figref id="DRAWINGS">FIG. 3</figref> depicts a diagram illustrating a modified example of the microlens array in the embodiment in which the present invention is applied. A microlens array <b>2</b> shown in the same drawing includes a microlens array substrate <b>50</b> having a plurality of concave lenses <b>52</b> formed thereon. On the side of the microlens array substrate <b>50</b> having the lenses <b>52</b> formed thereon, a light transmitting layer <b>54</b> is formed. The details described in the above-mentioned embodiment can be applied to the materials and forming methods of the light transmitting layer <b>54</b>. The light transmitting layer <b>54</b> is formed with a flat surface <b>56</b>. On the light transmitting layer <b>54</b>, at least one of a black matrix <b>42</b>, an electrode <b>44</b>, and an alignment layer <b>46</b> is formed, similarly to that shown in FIG. <b>2</b>(B). This modified example can also provide the same effects as the above-mentioned embodiment.

<figref id="DRAWINGS">FIG. 4</figref> depicts a diagram illustrating part of a liquid crystal projector as one example of a display device in which the microlens array of the present invention is applied. This liquid crystal projector has a light valve <b>60</b> incorporating the microlens array <b>1</b> fabricated by the method in the embodiment described above and a lamp <b>70</b> as a light source.

The microlens array <b>1</b> is arranged so that the lenses <b>12</b> are concave when seen from the lamp <b>70</b>. Additionally, a TFT substrate <b>62</b> is spaced from the alignment layer <b>46</b> by a gap. On the TFT substrate <b>62</b>, transparent discrete electrodes <b>64</b> and thin-film transistors <b>66</b> are disposed. An alignment layer <b>68</b> is deposited thereon. Furthermore, the TFT substrate <b>62</b> is arranged with the alignment layer <b>68</b> facing the alignment layer <b>46</b>.

Liquid crystal <b>61</b> is sealed between the alignment layers <b>46</b> and <b>68</b>. The liquid crystal <b>61</b> is driven by a voltage that is controlled by the thin-film transistors <b>66</b>.

According to this liquid crystal projector, light <b>72</b> irradiated from the lamp <b>70</b> is focussed at the lenses <b>12</b> at every pixel. Thus, a brighter screen can be displayed.

Moreover, as a precondition, it is necessary that the optical refractive index na of the light transmitting layer <b>32</b> and the optical refractive index nb of the microlens array substrate <b>10</b> have the relationship:

na&lt;nb.

When this condition is satisfied, the light is allowed to enter the medium having the smaller refractive index from the medium having the greater refractive index. The light <b>72</b> is refracted so as to bend away from the normal of the interface of both media to be focussed. Thus, the screen can be made brighter.

<figref id="DRAWINGS">FIG. 5</figref> depicts a diagram illustrating part of a liquid crystal projector as one example of a display device in which the microlens array of the present invention is applied. This liquid crystal projector has a light valve <b>80</b> incorporating the microlens array <b>2</b> fabricated by the method in the modified example described above and a lamp <b>70</b> as a light source.

The microlens array <b>2</b> is arranged so that the lenses <b>52</b> are convex when seen from the lamp <b>70</b>. Additionally, a TFT substrate <b>62</b> is spaced from the alignment layer <b>46</b> by a gap. On the TFT substrate <b>62</b>, transparent discrete electrodes <b>64</b> and thin-film transistors <b>66</b> are disposed. An alignment layer <b>68</b> is deposited thereon. Furthermore, the TFT substrate <b>62</b> is arranged with the alignment layer <b>68</b> facing the alignment layer <b>46</b>.

Liquid crystal <b>61</b> is sealed between the alignment layers <b>46</b> and <b>68</b>. The liquid crystal <b>61</b> is driven by a voltage that is controlled by the thin-film transistors <b>66</b>.

According to this liquid crystal projector, light <b>72</b> irradiated from the lamp <b>70</b> is focussed at lenses <b>52</b> at every pixel. Thus, a brighter screen can be displayed.

Moreover, as a precondition, it is necessary that the optical refractive index na of the light transmitting layer <b>54</b> and an optical refractive index nb of the microlens array substrate <b>50</b> have the relationship,

na&gt;nb.

When this condition is satisfied, the light is allowed to enter the medium having the greater refractive index from the medium having the smaller refractive index. The light <b>72</b> is refracted so as to bend towards the normal of the interface of both media to be focussed. Thus, the screen can be made brighter.

The microlens array in the invention can be applied to optical devices other than display devices, and can be applied to imaging devices, for example. The imaging devices have an image pickup device (image sensor). Light focussed by the microlens array enters the image pickup device. As the image pickup device, a CCD (Charge Coupled Device) type is named.

The invention is not limited to the embodiments described above; various modifications are possible. Additionally, the method for fabricating the microlens array substrate mentioned above is not limited in the invention, but the microlens array substrate can be fabricated as follows, for example.

(First method for fabricating microlens array substrate)

Next, FIGS. <b>6</b>(A) to <b>9</b>(C) depict diagrams illustrating one example of the method for fabricating the microlens array substrate.

(Master plate fabricating process)

FIGS. <b>6</b>(A) to <b>6</b>(E) depict diagrams illustrating the steps of producing a master plate for fabricating the microlens array substrate. The master plate <b>20</b> described in the embodiment mentioned above may be called a second master plate and the master plate described here may be referred as a first master plate.

First, as shown in FIG. <b>6</b>(A), a resist layer <b>114</b> is deposited on a substrate <b>112</b>. The substrate <b>112</b> will have its surface etched to form a master plate <b>110</b> (see FIG. <b>6</b>(E)). The etchable material is not particularly limited, but silicon or quartz is preferable because highly accurate curved surface parts <b>119</b> can be easily formed by etching (see FIG. <b>6</b>(E)).

As the material for forming the resist layer <b>114</b>, for example, commercially available positive resists of a cresol novolac resin mixed with a diazonaphthoquinone derivative as a sensitizer, which is generally used in fabricating semiconductor devices, can be used. Here, the positive resist is a substance that is exposed to radiation in accordance with a predetermined pattern and thereby the areas exposed to the radiation can be removed selectively by a developer.

As methods for depositing the resist layer <b>114</b>, methods of spin coating, dipping, spray coating, roll coating, and bar coating can be utilized.

Then, as shown in FIG. <b>6</b>(B), a mask <b>116</b> is arranged above the resist layer <b>114</b> and only the predetermined areas of the resist layer <b>114</b> are exposed to radiation <b>118</b> through the mask <b>116</b>.

The mask <b>116</b> is formed with patterns so as to transmit the radiation <b>118</b> only to the areas where it is necessary to form the curved surface parts <b>119</b> shown in FIG. <b>6</b>(E).

Additionally, as the radiation, light having a wavelength ranging from 200 to 500 nm is preferably used. The use of light in this wavelength region can utilize photolithography techniques established in liquid crystal panel fabrication processes and equipment utilized therefore, which can reduce costs.

Subsequently, after the resist layer <b>114</b> is exposed to the radiation <b>118</b>, it is subjected to a development process under predetermined conditions. Then, as shown in FIG. <b>6</b>(C), only the resist layer <b>114</b> in exposed areas <b>117</b> to the radiation <b>118</b> is selectively removed to reveal the surface of the substrate <b>112</b>. The areas other than those areas remain covered with the resist layer <b>114</b>.

The resist layer <b>114</b> is thus patterned, and the substrate <b>112</b> is etched to a predetermined depth using this resist layer <b>114</b> as a mask, as shown in FIG. <b>6</b>(D).

Specifically, isotropic etching where etching proceeds in all directions is applied to the areas revealed by the resist layer <b>114</b> on the substrate <b>112</b>. For example, wet etching is applied by dipping the substrate <b>112</b> into a chemical solution (etchant), thereby conducting isotropic etching. When quartz is used as the substrate <b>112</b>, etching is conducted by using an aqueous solution (buffered hydrofluoric acid) mixed with hydrofluoric acid and ammonium fluoride, for example. Isotropic etching is conducted and thereby the concave curved surface parts <b>119</b> are formed in the substrate <b>112</b>. Furthermore, the curved surface parts <b>119</b> are formed to have a curved surface which is the same as the inverted shape of the lenses <b>12</b> of the microlens array substrate <b>10</b> (see FIG. <b>1</b>(A)).

Then, the resist layer <b>114</b> is removed after etching has been completed. The substrate <b>112</b> has the curved surface parts <b>119</b> formed as shown in FIG. <b>6</b>(E), and is used as the master plate <b>110</b>.

After producing this master plate <b>110</b>, it can be used many times, as long as the durability permits. Therefore, it is economical. Additionally, the process of producing the master plate <b>110</b> can be omitted in the fabricating process of the second microlens array substrate or later, which allows a reduction in the number of steps and the cost.

In the embodiment described above, the positive resist was used in forming the curved surface parts <b>119</b> on the substrate <b>112</b>. However, a negative resist where areas exposed to radiation are insoluble and areas not exposed to radiation are selectively removable by developers may be used. In this case, a mask having a reverse pattern with respect to that of the above-mentioned mask <b>116</b> is used. Alternatively, without using mask, the resist may be directly exposed to laser light or electron beams in a pattern.

(Intermediate plate producing process)

FIGS. <b>7</b>(A) to <b>7</b>(C) depict diagrams illustrating the steps of producing the intermediate plate. First, as shown in FIG. <b>7</b>(A), an intermediate plate precursor <b>122</b> is placed on the side of the master plate <b>110</b> having the curved surface parts <b>119</b>. Then, a reinforcing plate <b>120</b> is brought into close contact with the master plate <b>110</b> with this intermediate plate precursor <b>122</b> therebetween. Thus, the intermediate plate precursor <b>122</b> is spread over a predetermined region to form a layer made of the intermediate plate precursor <b>122</b> between the master plate <b>110</b> and the reinforcing plate <b>120</b>, as shown in FIG. <b>7</b>(B).

Here, the intermediate plate precursor <b>122</b> is placed on the master plate <b>110</b>, but it may be placed on the reinforcing plate <b>120</b> or on both the master plate <b>110</b> and the reinforcing plate <b>120</b>. Alternatively, the intermediate plate precursor <b>122</b> may be spread over a predetermined region beforehand on either the master plate <b>110</b> or the reinforcing plate <b>120</b>, or on both, by methods of spin coating, spray coating, roll coating, bar coating or dipping.

The reinforcing plate <b>120</b> is for reinforcing an intermediate plate <b>124</b>, and is not particularly limited as long as it has process resistance in a process for producing the intermediate plate <b>124</b> or for producing a replica plate <b>130</b> from the intermediate plate <b>124</b>. For example, substrates made of quartz, glass, resin, metal, or ceramic can be utilized. Furthermore, when the intermediate plate <b>124</b> has suitable process resistance by itself, the reinforcing plate <b>120</b> is not needed.

As the intermediate plate precursor <b>122</b>, it is not particularly limited as long as the substance has excellent releasability from the master plate <b>110</b> and transferability of the shape of the curved surface parts <b>119</b>, has process resistance in the subsequent process for producing a replica plate <b>130</b> from the intermediate plate <b>124</b>, and has excellent transferability of the shape of curved surface parts <b>126</b> from the intermediate plate <b>124</b> to the replica plate <b>130</b>. As the intermediate plate precursor <b>122</b>, materials that can be selected as the light transmitting layer precursor <b>30</b>, described in the above-mentioned embodiment, may be used. These substances are preferable because they have an excellent releasability from silicon or quartz, which is superior as a master plate material in that highly accurate etching can be performed on it.

Moreover, as resins having plasticity, resins having thermoplasticity such as polycarbonate resins, polymethyl methacrylate resins, and amorphous polyolefine resins can be utilized. Such a resin is heated at the softening point temperature or above and thereby it is plasticated and liquefied. After it is sandwiched between the master plate <b>110</b> and the reinforcing plate <b>120</b>, as shown in FIG. <b>7</b>(B), the plasticated resin is cooled to be cured. Then, the intermediate plate <b>124</b> is formed.

The master plate <b>110</b> is brought into close contact with the reinforcing plate <b>120</b> with the intermediate plate precursor <b>122</b> therebetween. Thereby, the intermediate plate precursor <b>122</b> is formed into a shape corresponding to the curved surface parts <b>119</b> of the master plate <b>110</b>. Additionally, when the master plate <b>110</b> is attached to the reinforcing plate <b>120</b>, pressure may be applied via at least one of the master plate <b>110</b> and the reinforcing plate <b>120</b>, if necessary.

Applying pressure can reduce the length of time for spreading the intermediate plate precursor <b>122</b> over a predetermined region. Thereby, workability is improved and filling of the curved surface parts <b>119</b> is ensured.

Then, curing treatment is applied in accordance with the intermediate plate precursor <b>122</b>. For example, when a light-curable resin is used, light is radiated under predetermined conditions. Thereby, the intermediate plate precursor <b>122</b> is cured to form the intermediate plate <b>124</b>, as shown in FIG. <b>7</b>(B).

Subsequently, as shown in FIG. <b>7</b>(C), the intermediate plate <b>124</b> is released from the master plate <b>110</b>; and the reinforcing plate <b>120</b> is released, if necessary. The intermediate plate <b>124</b> thus obtained has convex curved surface parts <b>126</b> corresponding to the concave curved surface parts <b>119</b> of the master plate <b>110</b> formed therein.

(Replica plate production process)

FIGS. <b>8</b>(A) to <b>8</b>(C) depict diagrams illustrating the steps of producing the replica plate from the intermediate plate. First, as shown in FIG. <b>8</b>(A), a metal film <b>132</b> is deposited on the side of the intermediate plate <b>124</b> having the curved surface parts <b>126</b> formed thereon and its surface is made to be conductive (a conductor). As the metal film <b>132</b>, for example, nickel (Ni) may be formed to have a thickness of 500 to 1000 angstroms (10¹⁰m). As a method for depositing the metal film <b>132</b>, spattering, CVD, evaporation, and electroless plating methods can be used. Additionally, when the surface of the intermediate plate <b>124</b> has conductivity required for depositing metal layers by the subsequent electroforming method, it is not necessary to form this conductor.

Then, the metal film <b>132</b> is used as a cathode and a tip- or ball-like Ni is used as an anode. Ni is further electrodeposited by electroforming to form a thick metal layer <b>134</b>, as shown in FIG. <b>8</b>(B). The following shows one example of an electroplating solution:

Nickel sulfamate: 550 g/l

Boric acid: 35 g/l

Nickel chloride: 5 g/l

Leveling agent: 20 mg/l.

Subsequently, as shown in FIG. <b>8</b>(C), the metal film <b>132</b> and the metal layer <b>134</b> are released from the intermediate plate <b>124</b>, and they are cleaned, if necessary, thus obtaining the replica plate <b>130</b>. The replica plate <b>130</b> is formed with concave curved surface parts <b>136</b> corresponding to the convex curved surface parts <b>126</b> of the intermediate plate <b>124</b>. The curved surface parts <b>136</b> have a reverse pattern for forming lenses <b>142</b> shown in FIG. <b>9</b>(C) by transfer.

Furthermore, the metal film <b>132</b> may be removed from the replica plate <b>130</b> by applying a stripping treatment, as necessary.

(Light transmitting layer forming process)

Next, FIGS. <b>9</b>(A) to <b>9</b>(C) depict diagrams illustrating the step of forming the light transmitting layer having a plurality of lenses.

First, as shown in FIGS. <b>9</b>(A) and <b>9</b>(B), the replica plate <b>130</b> is brought into close contact with a reinforcing plate <b>144</b> with a light transmitting layer precursor <b>138</b> therebetween. This light transmitting layer precursor <b>138</b> is the material for the microlens array substrate. This light transmitting layer precursor <b>138</b> may be called a first light transmitting layer precursor and the light transmitting layer precursor <b>30</b> shown in <figref id="DRAWINGS">FIG. 1</figref> may be referred as a second light transmitting layer precursor.

This step is the same as the step illustrated in FIGS. <b>7</b>(A) to <b>7</b>(B). The light transmitting layer precursor <b>138</b> can also be selected from the substances that are selectable as the intermediate plate precursor <b>122</b> shown in FIG. <b>7</b>(A), but the substance must be transparent. Particularly, acrylic resins are preferable because they cure in a short time with light irradiation by utilizing various precursors or sensitizers (photopolymerization initiator) commercially available and can produce the microlens array substrate <b>10</b> having excellent optical characteristics.

Additionally, the reinforcing plate <b>144</b> is not particularly limited as long as it satisfies optical physical properties such as transparency or mechanical strength required for the microlens array substrate. For example, quartz or glass, or plastic substrates or films such as polycarbonate, polyallylate, poly(ethersulfone), polyethylene terephthalate, polymethyl methacrylate, and amorphous polyolefine can be utilized. Furthermore, when the microlens array substrate <b>10</b> can satisfy physical properties such as mechanical strength required for the substrate by itself, the reinforcing plate <b>144</b> is not needed.

The light transmitting layer thus formed on the replica plate <b>130</b> will become the microlens array substrate <b>10</b>. Moreover, the light transmitting layer constituting this microlens array substrate <b>10</b> may be called a first light transmitting layer and the light transmitting layer <b>32</b> shown in FIG. <b>1</b>(B) may be referred as a second light transmitting layer.

Then, as shown in FIG. <b>9</b>(C), the microlens array substrate <b>10</b> and the reinforcing plate <b>144</b> are released from the replica plate <b>130</b> in one piece. In addition, the reinforcing plate <b>144</b> is released from the microlens array substrate <b>10</b>, as necessary. According to the processes described above, the microlens array substrate <b>10</b> can be obtained.

In short, the processes described above are the method by which the intermediate plate <b>124</b> is produced from the master plate <b>110</b> having the curved surface parts <b>119</b>, the replica plate <b>130</b> is replicated based on the intermediate plate <b>124</b>, and the entire replica plate <b>130</b> produced is used to fabricate the microlens array substrate <b>10</b> reinforced by the reinforcing plate <b>144</b>. According to this, the expensive master plate <b>110</b> is used only when the intermediate plate <b>124</b> is produced. Thus, the frequency of producing the master plate <b>110</b> again due to its deterioration is reduced and the fabrication costs of the microlens array in a general sense can be decreased. Additionally, the replica plate <b>130</b> is not directly produced from the master plate <b>110</b>. Thus, the choice of materials for both plates is widened and the degree of freedom for methods of producing the replica plate <b>130</b> is increased. Therefore, transfer of the shapes of the curved surface parts <b>126</b> and <b>136</b> with high accuracy can be facilitated. Furthermore, enhancement of the durability of the master plate <b>110</b> and the replica plate <b>130</b> can be facilitated.

(Second method for fabricating microlens array substrate)

FIGS. <b>10</b>(A) to <b>11</b>(C) depict diagrams illustrating another example of the method for fabricating the microlens array substrate. The fabrication method described above is a method for fabricating microlens array substrates having convex lenses. However, when the microlens array substrate having concave lenses is to be fabricated, the curved surface parts <b>119</b> of the master plate <b>110</b> need to have a convex shape. Here, a method for producing a master plate having convex curved surface parts will be described as follows.

First, as shown in FIG. <b>10</b>(A), a resist layer <b>214</b> is deposited on a substrate <b>212</b>. This step and materials for the substrate <b>212</b> and the resist layer <b>214</b> are the same as those of the fabrication method described above.

Then, as shown in FIG. <b>10</b>(B), a mask <b>216</b> is arranged above the resist layer <b>214</b> and only predetermined areas of the resist layer <b>214</b> are exposed to radiation <b>218</b> through the mask <b>216</b>. The mask <b>216</b> is formed with patterns so as to transmit the radiation <b>218</b> only in the areas where it is necessary to form curved surface parts <b>219</b>, as shown in FIG. <b>11</b>(C).

Subsequently, after the resist layer <b>214</b> is exposed to the radiation <b>218</b>, it is subjected to a development process under predetermined conditions. Then, only the resist layer <b>214</b> in exposed areas <b>217</b> to the radiation <b>218</b> is selectively removed to reveal the surface of the substrate <b>212</b> and areas other than those remain covered with the resist layer <b>214</b>.

The resist layer <b>214</b> is thus patterned and the resist layer <b>214</b> is heated in a reflow process. Then, the resist layer <b>214</b> is melted by heat and the surface of the resist layer <b>214</b> is formed to have curved surfaces by surface tension, as shown in FIG. <b>10</b>(D).

Subsequently, as shown in FIG. <b>10</b>(E), the substrate <b>212</b> is etched to a predetermined depth by an etchant <b>220</b> using this resist layer as a mask. Specifically, anisotropic etching or dry etching such as reactive ion etching (RIE) is conducted.

FIGS. <b>11</b>(A) to <b>11</b>(C) depict diagrams illustrating a process of the substrate being etched. The substrate <b>212</b> is partially covered with the resist layer <b>214</b> having curved surfaces. The substrate <b>212</b> is first etched in the areas not covered with the resist layer <b>214</b>. Then, the resist layer <b>214</b> is etched by the etchant <b>220</b> and is gradually made smaller from an area indicated by a chain double-dashed line to an area indicated by a continuous line, as shown in FIGS. <b>11</b>(A) and <b>11</b>(B). At this time, the resist layer <b>214</b> has curved surfaces. Therefore, the resist layer <b>214</b> in this shape is gradually made smaller and then the substrate <b>212</b> is revealed little by little; the revealed areas are etched continuously and gradually. In this manner, the substrate <b>212</b> is etched continuously and gradually and thus the surface shape of the substrate <b>212</b> after etching is formed to have a curved surface. Lastly, as shown in FIG. <b>11</b>(C), the substrate <b>212</b> is formed with convex curved surface parts <b>219</b> and a master plate <b>210</b> can be obtained.

Once this master plate <b>210</b> has been produced, it can also be used repeatedly after that, as long as its durability permits. Therefore, it is economical. Additionally, the production process of the master plate <b>210</b> can be omitted in the fabrication process of the second microlens array or later, which can reduce the number of steps and save costs.

The microlens array substrate <b>2</b> (see <figref id="DRAWINGS">FIG. 3</figref>) can be fabricated by using this master plate <b>210</b> and by applying the processes described above. In this case, the details described above can also be applied here. The entire disclosure of Japanese Patent Application 2000-226675, filed Jul. 27, 2000 is herein incorporated by reference.